4-Stroke engine control device and control method

ABSTRACT

An atmospheric pressure is obtained from an intake pressure resulting immediately before an intake stroke, an injection fuel pressure P is calculated which is constituted by a differential pressure between a fuel pressure which is supplied to an injector  13  from the atmospheric pressure so obtained, a pump delivery pressure and the intake pressure and the intake pressure which is an injection atmosphere, a fuel injection time coefficient Q t0  per unit mass which is metered when a reference injection fuel pressure is P 0  is divided by a square root P 1/2  of the injection fuel pressure to calculate a fuel injection coefficient Q t , and a fuel injection time required to attain a desired air-fuel ratio is calculated using the fuel injection coefficient Q t  so calculated, whereby it is possible to realize a highly accurate control of the fuel injection time when a regulator for regulating an upper limit value for a fuel pump delivery pressure is provided on a fuel tank side.

TECHNICAL FIELD

This invention relates to an engine control device for controlling anengine and, more particularly to an engine control device suitable forcontrolling an engine provided with a fuel injection device forinjecting fuel.

BACKGROUND ART

With the widespread of fuel injection devices called injector in recentyears, control of fuel injection timing and fuel injection amount,namely, the air-fuel ratio has become easy, which makes it possible toimprove engine output and fuel consumption and to clean exhaust gas. Asto the fuel injection timing, it is common that a phase state of acamshaft, a state of an intake valve, to be exact, is detected, and,based on the detected result, fuel is injected. However, a cam sensorfor detecting the phase state of the camshaft, which is expensive andincreases the size of a cylinder head, is difficult to employ inmotorcycles or the like, in particular. To solve this problem, an enginecontrol device adapted to detect a phase state of a crankshaft and anintake pipe pressure and, based on those, to detect a stroke state of acylinder is proposed in JP-A-H10-227252. With this prior art, it ispossible to detect a stroke state of a cylinder without detecting aphase of a camshaft, so that it is possible to control fuel injectiontiming based on the stroke state.

To inject fuel from a fuel injection device as mentioned above, the fuelin the fuel tank must be pressurized by a fuel pump before supplied tothe fuel injection device. As is well known, since the pressure of thefuel pressurized by the pump fluctuates, a pressure control valve calledregulator is used to provide an upper limit on the fuel pressure. In thecase of a motorcycle, the regulator is generally provided in the closevicinity of the fuel injection device and is usually so constituted thata prescribed regulator control pressure usually set by a spring or thelike is added to the fuel on top of a pressure of an atmosphere intowhich the fuel is injected by the fuel injection device, for example, apressure in an intake pipe, as a back pressure. Thus, the fuel injectionpressure, which is a difference between the pressure of the fuelsupplied to the fuel injection device and the pressure of the atmosphereinto which the fuel is injected, is always equivalent to the regulatorcontrol pressure of the regulator.

However, when the regulator is provided in the close vicinity of thefuel injection device, a return line for returning surplus fuel from theregulator to the fuel tank must be provided for each fuel injectiondevice. Also, in most cases, the regulator is manufactured by the samemanufacturer of the pump but, when the pump and the regulator aredisposed separately, they are supplied separately. This increased thenumber of parts and makes cost reduction by making parts into assembliesimpossible. Then, it can be thought to place the regulator in thevicinity of the pump by, for example, making the pump and the regulatorinto an assembly. This constitution not only makes the return lineunnecessary but also makes it possible to reduce the number of parts andthe costs.

However, in the event that the regulator is disposed on the pump side ashas been described above, since the back pressure of the regulator isconstituted by the atmospheric pressure, where the atmospheric pressurechanges as the altitude changes, the fuel pressure also changes. Therehas been proposed a fuel injection control method which is described,for example, in JPA-A-S61-178526 as a method for compensating for achange in fuel pressure caused when the atmospheric pressure fluctuates.In this fuel injection control method, an atmospheric pressure isdetected by an atmospheric pressure sensor, whereby the fuel injectionamount is corrected based, for example, on a ratio between a referenceatmospheric pressure and an atmospheric pressure so detected. Accordingto this method, while the fuel injection amount can be compensatedirrespective of the fluctuation of atmospheric pressure, the atmosphericpressure sensor is needed, and the number of components is increased bythe additional of such a component, this leading to an increase inproduction costs.

When the regulator is placed in the vicinity of the pump, the backpressure of the regulator must be ambient pressure, so that the pressureof the fuel supplied to the fuel injection device is generally constant(When the ambient pressure changes with altitude, for example, the fuelpressure is also changed.). On the other hand, when no surge tank isprovide in the intake pipe as in the case of motorcycles, the pressurein the intake pipe into which the fuel is injected, namely the pressureof the atmosphere into which the fuel is injected is changeable. Thismeans that the injection fuel pressure, which is the difference betweenthe pressure of the fuel supplied to the fuel injection device and thepressure of the atmosphere into which the fuel is injected, is unstable.When the injection fuel pressure is unstable, the amount of fuelinjected from the injection device per a unit time becomes unstable.This makes it impossible to obtain a fuel injection amount to attain adesired air-fuel ratio only by controlling the fuel injection time.

As a device for correcting the fuel injection amount based on aninjection fuel pressure, there is an engine control device disclosed inJA-A-H08-326581. The engine control device detects an injection fuelpressure, integrates it over a given period of time to obtain the areathereof, compares the area with reference area values, and corrects thefuel injection amount based on the comparison result. In this enginecontrol device, however, the infection fuel pressure must be integrated,so that the operation load is unavoidably large. Also, since thereference values with which the integral value of the injection fuelpressure is compared must be organized into a map for every operationstate of the engine and stored, a memory with a large capacity isneeded. Naturally, the operation load in withdrawing the maps and makingthe comparison is large.

The invention was made with a view to resolving the problems and anobject thereof is to provide a control device for a four-stroke enginewhich can accurately control the fuel injection amount and time at atransitional time while reducing an operational load related to thecontrol of fuel injection and which can attempt to reduce the number ofcomponents and production costs.

DISCLOSURE OF THE INVENTION

According to a first aspect of the Invention, there is proposed acontrol device for a four-stroke engine having an intake valve between acombustion chamber and an intake port and having at least one intakecontrol valve for one intake port of the combustion chamber, the controldevice comprising a pump for pressurizing a fuel in a fuel tank, aregulator opened to an atmospheric pressure for regulating an upperlimit value for the fuel pressurized by the pump, a fuel injectiondevice for injecting the fuel regulated an upper limit value thereof bythe regulator into the intake port, intake pressure detecting unit fordetecting an intake pressure between the intake control valve and thecombustion chamber, at least either atmospheric pressure detecting unitfor detecting an atmospheric pressure or pump delivery pressuredetecting unit for detecting the pressure of the fuel pressurized by thepump, and fuel injection control unit for controlling the fuel injectiondevice based on at least either of an atmospheric pressure detected bythe atmospheric pressure detecting unit and a fuel pressure detected bythe pump delivery pressure detecting unit and an intake pressuredetected by the intake pressure detecting unit, wherein the intakepressure detecting unit detects an intake pressure a plurality of timeswhile the four-stroke engine completes four strokes of intake stroke,compression stroke, expansion stroke and exhaust stoke, and the fuelinjection control unit calculates a fuel injection time based on atleast one of a plurality of intake pressure values detected by theintake pressure detecting unit so as to inject the fuel with aninjection initiating timing according to the fuel injection time socalculated.

According to a second aspect of the invention, there is proposed acontrol device for a four-stroke engine as set forth in the first aspectof the invention, wherein the pump and the regulator are disposed withinthe fuel tank.

According to a third aspect of the invention, there is proposed acontrol device for a four-stroke engine as set forth in the first orsecond aspect of the invention, wherein the intake pressure detectingunit detects the intake pressure at least when a fuel injection timecalculated by the fuel injection control unit is over or is about to beover.

According to a fourth aspect of the invention, there is proposed acontrol device for a four-stroke engine as set forth in any of the firstto third aspects of the invention, wherein only the pump deliverypressure detecting unit is provided.

According to a fifth aspect of the invention, there is proposed acontrol device for a four-stroke engine as set forth in any of the firstto third aspects of the invention, wherein only the atmospheric pressuredetecting unit is provided.

According to a sixth aspect of the invention, there is proposed acontrol device for a four-stroke engine as set forth in any of the firstto third aspects, or the fifth aspect of the invention, wherein theatmospheric pressure detecting unit detects an atmospheric pressure froman intake pressure detected by the intake pressure detecting unit.

According to a seventh aspect of the invention, there is proposed acontrol device for a four-stroke engine as set forth in any of the firstto third aspects, or in the fifth or sixth aspect of the invention,wherein the intake pressure detecting unit detects at least an intakepressure resulting immediately before the intake valve opens.

According to an eighth aspect of the invention, there is proposed amethod for controlling a four-stroke engine having an intake valvebetween a combustion chamber and an intake port and having at least oneintake control valve for one intake port of the combustion chamber, themethod comprising the steps of pressurizing a fuel in a fuel tank,regulating by a regulator opened to an atmospheric pressure an upperlimit value for the fuel pressurized by the pump, injecting the fuelregulated an upper limit value thereof by the regulator into the intakeport, detecting an intake pressure between the intake control valve andthe combustion chamber, performing at least either the step of detectingan atmospheric pressure or the step of detecting the pressure of thefuel so pressurized, and controlling the fuel injection based on atleast either an atmospheric pressure detected through the step ofdetecting an atmospheric pressure or a fuel pressure detected throughthe step of detecting a fuel pressure and an intake pressure detectedthrough the step of detecting an intake pressure, wherein in the step ofdetecting an intake pressure, an intake pressure is detected a pluralityof times while the four-stroke engine completes four strokes of intakestroke, compression stroke, expansion stroke and exhaust stoke, and inthe step of controlling the fuel injection, a fuel injection time iscalculated based on at least one of a plurality of intake pressurevalues detected through the step of detecting an intake pressure so thatthe fuel is injected with an injection initiating timing according tothe fuel injection time so calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating the configuration of amotorcycle engine and a control device therefor according to a firstembodiment of the invention.

FIG. 2 is a block diagram illustrating an operational processimplemented by the engine control unit shown in FIG. 1.

FIG. 3 is an explanatory view illustrating the detection of a strokestate from the phase of a crankshaft and an intake pressure.

FIG. 4 shows a map stored in an in-cylinder air mass calculating partfor calculating an in-cylinder air mass.

FIG. 5 shows a map stored in a target air-fuel ratio calculating partfor calculating a target air-fuel ratio.

FIG. 6 is an explanatory view illustrating the function of a transitioncorrection part.

FIG. 7 is an explanatory view illustrating a correlation between a crankangle or a stroke and an intake pressure.

FIG. 8 is an explanatory view illustrating a function between an engineload and an intake pressure immediately before an intake stroke.

FIG. 9 is an explanatory view illustrating a relationship among a fuelpressure, an intake pressure which is an ambient pressure and aninjection fuel pressure.

FIG. 10 is a schematic view illustrating the configuration a motorcycleengine and a control device therefor according to a second embodiment ofthe invention.

FIG. 11 is a block diagram illustrating an operational processimplemented by the engine control unit shown in FIG. 10.

FIG. 12 is a schematic view illustrating the configuration of amotorcycle engine and a control device therefore according to a thirdembodiment of the invention.

FIG. 13 is a block diagram illustrating an operational processimplemented by the engine control unit shown in FIG. 12.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described below.

FIG. 1 is a schematic diagram illustrating the configuration of, forexample, a motorcycle engine and a control device therefor according toa first embodiment of the invention. The engine 1 is a four-cylinder,four-cycle engine and has a cylinder body 2, a crankshaft 3, a piston 4,a combustion chamber 5, an intake pipe 6, an intake valve 7, an exhaustpipe 8, an exhaust valve 9, a spark plug 10, and an ignition coil 11.Note that the intake pipe 6, which is independent, is connected to eachof four combustion chambers 5, a throttle valve 12 which functions as anintake control valve which opens and closes according to the position oropening of the throttle valve 12 is provided in each intake pipe 6, andan injector 13, which functions as a fuel injection device, is provideda downstream side of the throttle valve 12 or a combustion chamber sideof the intake pipe 6. The injector 13 is connected to a filter 18, afuel pump 17 and a regulator 16 which are housed in a fuel tank 19. Theregulator 16 provides an upper limit on the pressure applied to the fuelby the fuel pump 17. A regulator housed in the fuel tank 19 is arrangedsuch that a prescribed regulator control pressure is applied with theambient pressure serving as the back pressure. Thus, when the pumpdelivery pressure is lower than the regulator control pressure, the pumpdelivery pressure (more accurately, the pump delivery pressure includingambient pressure as a back pressure) is the pressure of the fuelsupplied to the injector 13. The engine 1 employs an independent suctionsystem, so that the injector 13 is provided in each intake pipe 6 ofeach cylinder.

The operating state of the engine 1 is controlled by an engine controlunit 15. As means for performing control input into the engine controlunit 15, namely means for detecting the operating state of the engine 1,there are provided a crank angle sensor 20 for detecting the rotationalangle, namely phase, of the crankshaft 3, a cooling water temperaturesensor 21 for detecting the temperature of the cylinder body 2 orcooling water, namely the temperature of the engine body, an exhaustair-fuel ratio sensor 22 for detecting the air-fuel ratio in the exhaustpipe 8, a fuel pressure sensor 23 for detecting the fuel deliverypressure of the fuel pump 17 as the pressure of the fuel supplied to theinjector 13, an intake pipe pressure sensor 24 for detecting thepressure of intake air in the intake pipe 6, and an intake airtemperature sensor 25 for detecting the temperature in the intake pipe6, namely the temperature of intake air. The engine control unit 15receives detecting signals from the sensors and outputs control signalsto the fuel pump 17, the injector 13 and the ignition coil 11.

The engine control unit 15 is constituted of a microcomputer (not shown)and so on. FIG. 2 is a block diagram illustrating an embodiment of theengine control operation performed by the microcomputer in the enginecontrol unit 15. The engine control operation is performed by an enginerotational speed calculating part 26 for calculating the enginerotational speed based on a crank angle signal, a crank timing detectingpart 27 for detecting crank timing information, namely the stroke statebased on the crank angle signal and an intake pipe pressure signal, anincylinder air mass calculating part 28 for calculating the air mass inthe cylinder (amount of intake air) based on the crank timinginformation detected by the crank timing detecting part 27 together withan intake air temperature signal, an cooling water temperature (enginetemperature) signal, the intake pipe pressure signal and the enginerotational speed calculated by the engine rotational speed calculatingpart 26, a target air-fuel ratio calculating part 33 for calculating atarget air-fuel ratio based on the engine rotational speed calculated inthe engine rotational speed calculating part 26 and the intake pipepressure signal, a fuel injection amount calculating part 34 forcalculating the amount of fuel to be injected based on the targetair-fuel ratio calculated in the target air-fuel ratio calculating part33, the intake pipe pressure signal and the air mass in the cylindercalculated in the incylinder air mass calculating part 28, an ambientpressure calculating part 41 for calculating the ambient pressure basedon the intake pipe pressure signal and the crank timing informationdetected by the crank timing detecting part 27, a injection fuelpressure calculating part 42 for calculating the injection fuel pressurebased on the ambient pressure calculated in the ambient pressurecalculating part 41, the pressure of fuel supplied to the injector 13detected by the fuel pressure sensor 23 and the intake pipe pressuresignal, a fuel injection coefficient calculating part 43 for calculatinga fuel injection coefficient based on the fuel injection pressurecalculated in the fuel injection pressure calculating part 42, a fuelinjection time calculating part 44 for calculating the fuel injectiontime based on the amount of fuel to be injected calculated in the fuelinjection amount calculating part 34 and the fuel injection coefficientcalculated in the fuel injection coefficient calculating part 43, aninjection pulse output part 30 for outputting injection pulses to theinjector 13 based on the fuel injection time calculated in the fuelinjection time calculating part 44 and the crank timing informationdetected by the crank timing detecting part 27, an ignition timingcalculating part 31 for calculating ignition timing based on the enginerotational speed calculated in the engine rotational speed calculatingpart 26 and the target air-fuel ratio set in the target air-fuel ratiocalculating part 33, and an ignition pulse output part 32 for outputtingignition pulses corresponding to the ignition timing set in the ignitiontiming calculating part 31 to the ignition coil 11 based on the cranktiming information detected by the crank timing information detectingpart 27.

The engine rotational speed calculating part 26 calculates therotational speed of the crankshaft as an output shaft of the engine asthe engine rotational speed based on the rate of change of the crankangle signal with time.

The crank timing detecting part 27, which has a constitution similar tothe stroke judging device disclosed in JA-A-H10-227252, detects thestroke state of each cylinder as shown in FIG. 3, for example, andoutputs it as crank timing information. Namely, in a four-cycle engine,the crankshaft and the camshaft are constantly rotated with a prescribedphase difference, so that when crank pulses are read with respect toeach 30 degrees rotation of the crank shaft as shown in FIG. 3, thecrank pulse “4” represents either an exhaust stroke or a compressionstroke. As is well known, during an exhaust stroke, the exhaust valve isclosed and the intake valve is opened, so that the intake pipe pressureis high. However, in an initial stage of a compression stroke, theintake pipe pressure is low because the intake valve is still open orbecause of the previous intake stroke even if the intake valve isclosed. Thus, the crank pulse “4” outputted when the intake pipepressure is low indicates that a second cylinder is in a compressionstroke, and when the crank pulse “3” is obtained, the second cylinder isat the intake bottom dead center. When the stroke state of one of thecylinders can be detected as above, since there are prescribed phasedifferences between the strokes of the cylinders, the stroke state ofthe other cylinders can be determined. For example, the first crankpulse “9” after the crank pulse “3” indicating that the second cylinderis at its intake bottom dead center indicates that the first cylinder isat its intake bottom dead center, the first clank pulse “3” after thatindicates that the third cylinder is at its intake bottom dead center,and the first clank pulse “9” after that indicates that the fourthcylinder is at its intake bottom dead center. Then, when the intervalsbetween the pulses are interpolated with the rotational speed of thecrankshaft, the present stroke state can be detected in further detail.

The incylinder air mass calculating part 28 has a three-dimensional mapas shown in FIG. 4 for use in calculating the air mass in the cylinderbased on the intake pipe pressure signal and the engine rotational speedcalculated in the engine rotational speed calculating part 26. The threedimensional map of the incylinder air mass can be obtained only bymeasuring air mass in the cylinder while changing the intake pipepressure with the engine rotated at a prescribed rotational speed. Themeasurement can be conducted with a relatively simple experiment, sothat the map can be organized with ease. The map could be organized withan advanced engine simulation system. The incylinder air mass, which ischanged with engine temperature, may be corrected with the cooling watertemperature (engine temperature) signal.

The target air-fuel ratio calculating part 33 has a three-dimensionalmap as shown in FIG. 5 for use in calculating the target air-fuel ratiobased on the intake pipe pressure signal and the engine rotational speedcalculated in the engine rotational speed calculating part 26. Thethree-dimensional map can be organized on paper to some extent. Ingeneral, the air-fuel ratio is correlated with torque. When the air-fuelratio is low, namely, when the amount of fuel is large and the amount ofair is small, the torque increases but the efficiency decreases.Whereas, when the air-fuel ratio is high, namely, when the amount offuel is small and the amount of air is large, the torque decreases butthe efficiency increases. The state where the air-fuel ratio is low iscalled “rich” and the state where the air-fuel ratio is high is called“lean”. The leanest state is one often referred to as “stoichiometry”,where the ideal air-fuel ratio at which complete combustion of gasolinetakes place, namely, an air-fuel ratio of 14.7 is attained.

The engine rotational speed is one of parameters indicating runningconditions of the engine, and in general, a larger air-fuel ratio isemployed at a higher end of the engine rotational speed, whereas asmaller air-fuel ratio is employed at a lower end of the enginerotational speed. This is intended to enhance the responsecharacteristic of the engine torque at the lower end of the engine speedand to enhance the response characteristic of the engine speed at thehigher end of the engine speed. In addition, the intake pressure is oneof parameters indicating the loaded conditions of the engine such as thethrottle position or opening, and in general, a smaller air-fuel ratiois employed when the engine load becomes heavy, that is, when thethrottle opening is narrow and the intake pressure is high, whereas alarger air-fuel ratio is employed when the engine load is light, thatis, when the throttle opening is wide and the intake pressure is low.This is because an emphasis is put on the torque with the heavy engineload, whereas an emphasis is put on the efficiency with the light engineload.

As above, the target air-fuel ratio has a physical meaning easy tounderstand and thus can be set to some extent in accordance withrequired engine output characteristics. It is needless to say that theair-fuel ratio may be tuned in accordance with the outputcharacteristics of an actual engine.

The target air-fuel ratio calculating part 33 has a transitioncorrection part 29 for detecting transitions, more specifically,acceleration and deceleration of the engine from the intake pipepressure signal and correcting the target air-fuel ratio. For example,as shown in FIG. 6, the change of the intake pipe pressure is also aresult of an operation of the throttle, so that an increase of theintake pipe pressure indicates that the throttle is opened to acceleratethe vehicle, namely, the engine is accelerating. When such anaccelerating state is detected, the target air-fuel ratio is set to therich side temporally and then returned to the original target value. Asa method to return the air-fuel ratio to the original value, there maybe employed any existing method, such as a method in which a weighingcoefficient of a weighted mean of the air-fuel ratio set to the leanside and the original target air-fuel ratio is gradually changed. When adeceleration state is detected, the target air-fuel ratio may be set tothe lean side than the original target air-fuel ratio to attain highefficiency.

Note that an intake pressure detected at a predetermined crank timingsubstantially before the top dead center in a compression stroke wasused in setting a target air-fuel ratio using the target air-fuel ratiocalculating part 33. In this embodiment, as will be described later on,when detecting an atmospheric pressure, an intake pressure is used whichis detected at a predetermined crank timing before the top dead centerin an exhaust stroke, to be specific, immediately before an intakestroke or immediately before the intake valve opens. In addition, whendetecting an injection fuel pressure, an intake pressure is used whichis detected when the fuel injection time is over or is about to be over.Consequently, intake pressures need to be detected at least a pluralityof times in the four strokes of intake, compression, expansion andexhaust strokes. Thus, by detecting intake pressures a plurality oftimes, as has been described previously, an acceleration demand byopening the throttle valve or a transition can be detected.

The ambient pressure calculating part 41 calculates the ambient pressurebased on the intake pipe pressure signal and the crank timinginformation. FIG. 7 is a graph of intake pipe pressure versus phase ofthe crankshaft, namely crank timing information. Each of the curvescorresponds to the engine load at the time when the crank angle is−180°. For example, 45 kPa is the minimum engine load and 100 kPa is themaximum engine load. In FIG. 7, an intake stroke is started when thacrank angle is −360°. Immediately before the intake stroke, namely whenthe crank angle is near −360°, the intake pipe pressure is almost stableand is ambient as described later. In an engine without a supercharger,when the intake pipe pressure is stable, it is because the pressure isabout ambient. Thus, in this embodiment, the intake pipe pressureimmediately before the intake stroke, namely, immediately before theintake valve is opened is detected as the ambient pressure. However, asis clear from FIG. 7, when the engine load is large, the intake pipepressure is relatively unstable. Thus, the ambient pressure is detectedusing an intake pipe pressure at the time when the engine load is small.The intake pipe pressure of 45 kPa at the time when the crank angle is−180° indicates that the engine is nearly idling. In this state, theintake pressure is also unstable. Thus, it is preferred that the ambientpressure be detected using the intake pipe pressure at the time when theengine load is small except when the engine is idling.

FIG. 8 is a graph showing the relation between the intake pipe pressureimmediately before an intake stroke and the engine load with the enginerotational speed as a parameter, wherein the intake pipe pressure at thetime when the crank angle is −180°, namely the engine load is plotted inthe horizontal axis and the pressure immediately before an intake strokeis plotted in the vertical axis. As shown in FIG. 8, even if the engineload is the same, the intake pipe pressure immediately before an intakestroke can be different from the ambient pressure depending upon theengine rotational speed. Thus, to make it exact, the ambient pressuremay be detected using the engine rotational speed as one of theparameters by, for example, a method in which the ambient pressure isdetected from the intake pipe pressure immediately before an intakestroke only when the rotational speed has reached a predetermined value.

The injection fuel pressure calculating part 42 calculates the injectionfuel pressure, which is the difference between the fuel pressure and thepressure of the atmosphere into which the fuel is injected, based on theintake pipe pressure, the pump delivery pressure, and the ambientpressure calculated in the ambient pressure calculating part 41 and soon. FIG. 9 is a graph showing the relation among the fuel pressure, theintake pipe pressure as the atmosphere pressure, and the injection fuelpressure. In the case where the fuel pump 17 and the regulator 16 isdisposed in the vicinity of the fuel tank as in this embodiment, thepump back pressure and the regulator back pressure are both ambient (thefuel tank is not completely airtight). The pump delivery pressure andthe regulator control pressure rise on top of the ambient pressure. Whenthe pump delivery pressure is smaller than the regulator controlpressure, the pump delivery pressure will be the fuel pressure. When thepump delivery pressure is the regulator control pressure or higher, theregulator control pressure will be the fuel pressure. After thecalculation of the injection fuel pressure by the above comparison, theinjection fuel pressure is calculated by subtracting the intake pipepressure (the pressure of the atmosphere into which the fuel isinjected) therefrom. In the case of a motorcycle, especially, since nosurge tank is provided in the intake pipe, the intake pipe pressurevaries greatly as shown in FIG. 9. Thus, in order to control the fuelinjection amount by the fuel injection time as described later, theinjection fuel pressure must be detected accurately. In this embodiment,the ambient pressure can be detected from the intake pipe pressure andthe injection fuel pressure can be accurately detected from the pumpdelivery pressure and the intake pipe pressure, as mentioned above.Also, since no ambient pressure sensor is needed, the cost can bereduced for that. Note that as an intake pressure used when calculatingthe injection fuel pressure the intake pressure is used which wasdetected when the previous fuel injection time was over or was about tobe over when implementing the operational process. This is because theamount of fuel injected from the injector 13 is most stable when thefuel injection time is over or is about to be over in the operationalprocess due to the delay in response of the injector 13, and as aresult, the intake pressure in the time zone becomes most stable.

Next, the fuel injection coefficient calculating part 43 calculates afuel injection coefficient for use in calculation of the fuel injectiontime based on the injection fuel pressure calculated in the injectionfuel pressure calculating part 42. The flow velocity v₁ of the fuelsupplied to the injector 13 can be regarded as substantially 0, theequation (1) is established by Bernoulli's theorem.

P ₁ =ρ·v ₂ ²/2+P ₂  (1)

wherein ρ is the density of the fuel, P₁ is the pressure of the fuelsupplied to the injector 13, namely the fuel pressure, v₂ is the flowvelocity of the fuel injected from the injector into the intake pipe andP₂ is the pressure of the atmosphere into which the fuel in injected,namely the intake pipe pressure.

When the equation is solved for v₂, the equation (2) is obtained:

v ₂=(2(P ₁ −P ₂)/ρ)^(1/2)  (2)

Here, (P₁−P₂) in the equation (2) is the injection fuel pressurecalculated in the injection fuel pressure calculating part 42. LettingP=(P₁−P₂), the fuel mass M injected from the injector 13 per a unit timecan be obtained from the equation (3):

M=S·v ₂ ·ρ=S·(2ρ·P)^(1/2)  (3)

wherein S is the cross-sectional area of the injection port of theinjector 13.

This indicates that the fuel mass M injected from the injector 13 per aunit time is in proportion to the square root of the injection fuelpressure P.

Then, setting a reference injection fuel pressure P₀ and letting Q_(t0)be a fuel injection coefficient (injection fuel flow rate characteristiccoefficient) which gives a unit mass of fuel to be injected when theinjection fuel pressure is the reference injection fuel pressure P₀, thefuel injection coefficient (injection fuel flow rate characteristiccoefficient) Q_(t) which gives a unit mass of fuel to be injected whenthe injection fuel pressure is P is given by the following equation (4):

Q _(t) =Q _(t0)×(P ₀ /P)^(1/2)  (4)

Thus, by multiplying the fuel injection amount by the fuel injectioncoefficient (injection fuel flow rate characteristic coefficient) Q_(t),the fuel injection time can obtained.

Thus, the fuel injection time calculating part 44 calculates the fuelinjection time T by multiplying the fuel injection amount V calculatedin the fuel injection amount calculating part 34 by the fuel injectioncoefficient (injection fuel flow rate characteristic coefficient) Q_(t).Namely, when letting the product of the injection fuel flow ratecharacteristic coefficient Q_(t0) obtained when the injection fuelpressure is the reference injection fuel pressure P₀, the fuel injectionamount V to attain a desired air-fuel ratio, and the square root P₀^(1/2) of the reference injection fuel pressure be a preset value, thefuel injection time T calculated through the arithmetic processperformed in the fuel injection time coefficient calculating part 43 andthe fuel injection time calculating part 44 is a value obtained bydividing the preset value by the square root of the injection fuelpressure, namely P^(1/2).

Then, the injection pulse output part 30 calculates a fuel injectioninitiating timing from crank timing information detected at the cranktiming detecting part 27 and outputs to the injector 13 an injectionpulse based on the fuel injection time calculated at the fuel injectiontime calculating part 44.

Thus, according to the embodiment of the invention, by performing thedetection of an intake pressure a plurality of times while thefour-stroke engine completes the four strokes of intake, compression,expansion and exhaust strokes thereof, a change in intake pressure everytime the strokes change can be detected to thereby detect a transition,thereby making it possible to have a target air-fuel ratio or to injectfuel according to the transition so detected. In addition, since anaccurate injection fuel pressure is detected using at least one of theplurality of intake pressure values detected, to be specific, an intakepressure at the optimum timing for calculating a fuel injection time,that is, at the time when the fuel injection is over or is about to beover in the operational process so that an accurate fuel injection timecan be set using the accurate injection fuel pressure so detected, fuelcan be injected with an optimum injection initiating timing so as toimprove the combustion efficiency.

In this embodiment, as described above, the regulator 16 is placed inthe vicinity of the fuel tank 19 together with the fuel pump 17, thedifference between the pressure of fuel supplied to the injector 13 andthe pressure of the atmosphere into which the fuel is injected, namelythe intake pipe pressure, is detected as the injection fuel pressure,and, based on the square root of the thus detected injection fuelpressure, the fuel injection time during which the fuel is injected fromthe injector 13 is controlled. Thus, since neither integration of theinjection fuel pressure nor a large number of maps are needed, theoperation load can be reduced. Also, it is possible to reduce the numberof parts and the costs by making the fuel pump 17 and the regulator 16into an assembly.

In addition, since the product of the fuel injection coefficient Q_(t0)resulting when the reference injection fuel pressure is P₀, the fuelinjection amount V required to attain the desired air-fuel ratio and thesquare root value P₀ ^(1/2) of the reference injection fuel pressurevalue is set to the preset value and the fuel injection time T iscalculated by dividing the preset value by the square root value P^(1/2)of the injection fuel pressure value, the fuel injection time requiredto attain the desired air-fuel ratio can be calculated and set easilyand accurately. Additionally, as a result, fuel can be injected with theoptimum fuel injection timing, whereby the combustion efficiency can beenhanced.

Additionally, since the injection fuel pressure is calculated based onthe intake pipe pressure as the pressure of the atmosphere into whichthe fuel is injected, the ambient pressure and the fuel pressure, it ispossible to detect the injection fuel pressure accurately and easily.Also, since the ambient pressure is calculated from the pressure in theintake pipe of the engine, there is no need to provide an ambientpressure sensor, making it possible to reduce the number of parts andthe costs. Additionally, since the intake pipe pressure immediatelybefore the intake valve of the engine is opened is calculated as theambient pressure, it is possible to detect the ambient pressureaccurately in real time.

Next, a second embodiment of a control device for a four-stroke engineaccording to the invention will be described. The description will bemade by reference to FIG. 10. In this embodiment, in addition to theconfiguration of the first embodiment, an atmospheric pressure sensor 14is added as an atmospheric pressure detecting unit. Thus, since, withthe provision of the atmospheric pressure sensor 14 which can detectdirectly an atmospheric pressure, there is no need to calculate anatmospheric pressure from an intake pressure as is done in the firstembodiment, an operational process that will be executed by the enginecontrol unit 15 becomes what is shown in FIG. 11, in which theatmospheric pressure calculating part 41 provided in the firstembodiment is removed and an atmospheric pressure signal detected by theatmospheric pressure sensor 14 is fetched to the injection fuel pressurecalculating part 42. Where atmospheric pressures can be detecteddirectly, as has been described above, the operational process ofcalculating an atmospheric pressure from an intake pressure can beomitted, and hence the operation load can be reduced by such an extent.

Next, a third embodiment of a control device for a four-stroke engineaccording to the invention will be described. The description will bemade by reference to FIG. 12. In this embodiment, the pump deliverypressure sensor 23 is removed from the configuration of the secondembodiment. As has been described previously, unless the lower limitvalue of the pump delivery pressure becomes smaller than the regulatorcontrol pressure, the fuel pressure remains equal to the regulatorcontrol pressure. In this embodiment, a pump having a sufficientdelivery pressure is used for the fuel pump 17 so that the lower limitvalue of the pump delivery pressure does not lower below the regulatorcontrol pressure, whereby the fuel pressure is made to be constantrelative to the regulator control pressure, thereby the pump deliverypressure sensor 23 being allowed to be removed. In the event that thepump delivery pressure sensor 23 can be omitted as has just beendescribed, the number of components involved and production costs can bereduced by such an extent. Note that an operational process that will beexecuted by the engine control unit 15 in this embodiment is what isshown in FIG. 13, in which the fuel injection pressure calculating part42 calculates an injection fuel pressure using the regulator controlpressure as the fuel pressure.

Note that while the engine of the type in which fuel is injected intothe intake port has been described in detail in the respectiveembodiments above, the control device for a four-stroke engine accordingto the invention can be applied to engines of a type in which fuel isinjected into cylinders, or, so-called engines of a direct injectiontype.

In addition, while the engine having four cylinders or the so-calledmulti-cylinder engine has been described in detail in the respectiveembodiments above, the control device for a four-stroke engine can beapplied to a single-cylinder engine.

Additionally, the engine control unit can be replaced by various typesof operational circuits instead of the microcomputer.

Moreover, while the pressure sensors which can detect pressures linearlyare used to detect the various pressures in the respective embodimentsabove, a pressure switch adapted to be on and off at a predeterminedpressure can also be combined to constitute the pressure detecting unit.

INDUSTRIAL APPLICABILITY

As has been described heretofore, according to the control device for afour-stroke engine of the first aspect of the invention, since the fuelinjection device is controlled based on at least either of theatmospheric pressure and the fuel pressure, and the intake pressure, theinjection fuel pressure required to control the fuel injection amount bythe fuel injection time can be detected accurately and easily. Inaddition, since intake pressures are detected a plurality of times whilethe four-stroke engine completes its four strokes of intake,compression, expansion and exhaust strokes, a change in intake pressureresulting every time the strokes change can be detected so as to detecta transition, whereby fuel can be injected according to the transitionso detected. Moreover, since a fuel injection time is calculated basedon at least one of the plurality of intake pressure values so detected,whereby fuel is injected with an injection initiating timing accordingto the fuel injection time so calculated, an accurate fuel injectiontime can be set using an intake pressure detected at a timing which isoptimum to calculate the fuel injection time, and as a result, fuel canbe injected with the optimum injection initiating timing so as toenhance the combustion efficiency.

In addition, according to the control device for a four-stroke engine ofthe second aspect of the invention, the pump and the regulator aredisposed within the fuel tank so as to be part of the fuel tankassembly, whereby the number of components to be assembled individuallyand hence production costs can be reduced.

Additionally, according to the control device for a four-stroke engineof the third aspect of the invention, since an intake pressure isdetected at least when the fuel injection time so calculated is over oris about to be over, a steady intake pressure resulting substantiallywhile fuel is being injected can be detected, whereby the fuel injectionpressure can be detected more accurately and easily.

Furthermore, according to the control device for a four-stroke engine ofthe fourth aspect of the invention, since the provision of only the pumpdelivery pressure detecting unit is made possible by adopting theconfiguration in which an atmospheric pressure is detected from anintake pressure, the necessity of the atmospheric pressure can beobviated, and the number of components involved and production costs canbe attempted to be reduced by such an extent.

Moreover, according to the control device for a four-stroke engine ofthe fifth aspect of the invention, since the provision of only theatmospheric pressure is made possible by adopting the configuration inwhich when the lower limit value of the pump delivery pressure is largerthan the control pressure of the regulator, the fuel pressure is made toconstitute the control pressure of the regulator, the necessity of thepump delivery pressure sensor is obviated, whereby the number ofcomponents involved and production costs can be attempted to be reducedby such an extent.

In addition, according to the control device for a four-stroke engine ofthe sixth aspect of the invention, since an atmospheric pressure isdetected from the detected intake pressure, there is no need to providean atmospheric pressure sensor separately, whereby the number ofcomponents involved and production costs can be attempted to be reducedby such an extent.

Additionally, according to the control device for a four-stroke engineof the seventh aspect of the invention, since at least an intakepressure resulting immediately before the intake valve opens isdetected, atmospheric pressures can be detected in real time andaccurately by calculating the intake pressure resulting immediatelybefore the intake valve opens as an atmospheric pressure.

In addition, according to the control method for a four-stroke engine ofthe eighth aspect of the invention, since the fuel injection device iscontrolled based on at least either of the atmospheric pressure and thefuel pressure, and the intake pressure, the injection fuel pressurerequired to control the fuel injection amount by the fuel injection timecan be detected accurately and easily. In addition, since intakepressures are detected a plurality of times while the four-stroke enginecompletes its four strokes of intake, compression, expansion and exhauststrokes, a change in intake pressure resulting every time the strokeschange can be detected so as to detect a transition, whereby fuel can beinjected according to the transition so detected. Moreover, since a fuelinjection time is calculated based on at least one of the plurality ofintake pressure values so detected, whereby fuel is injected with aninjection initiating timing according to the fuel injection time socalculated, an accurate fuel injection time can be set using an intakepressure detected at a timing which is optimum to calculate the fuelinjection time, and as a result, fuel can be injected with the optimuminjection initiating timing so as to enhance the combustion efficiency.

What is claimed is:
 1. A control device for a four-stroke engine havingan intake valve between a combustion chamber and an intake port andhaving at least one intake control valve for one intake port of thecombustion chamber, the control device comprising a pump forpressurizing a fuel in a fuel tank, a regulator opened to an atmosphericpressure for regulating an upper limit value for the fuel pressurized bythe pump, a fuel injection device for injecting the fuel regulated anupper limit value thereof by the regulator into the intake port, intakepressure detecting unit for detecting an intake pressure between theintake control valve and the combustion chamber, at least eitheratmospheric pressure detecting unit for detecting an atmosphericpressure or pump delivery pressure detecting unit for detecting thepressure of the fuel pressurized by the pump, and fuel injection controlunit for controlling the fuel injection device based on at least eitherof an atmospheric pressure detected by the atmospheric pressuredetecting unit and a fuel pressure detected by the pump deliverypressure detecting unit and an intake pressure detected by the intakepressure detecting unit, wherein the intake pressure detecting unitdetects an intake pressure a plurality of times while the four-strokeengine completes four strokes of intake stroke, compression stroke,expansion stroke and exhaust stoke, and the fuel injection control unitcalculates a fuel injection time based on at least one of a plurality ofintake pressure values detected by the intake pressure detecting unit soas to inject the fuel with an injection initiating timing according tothe fuel injection time so calculated.
 2. A control device for afour-stroke engine as set forth in claim 1, wherein the pump and theregulator are disposed with the fuel tank.
 3. A control device for afour-stroke engine as set forth claim 1 or 2, wherein the intakepressure detecting unit detects the intake pressure at least when a fuelinjection time calculated by the fuel injection control unit is over oris about to be over.
 4. A control device for a four-stroke engine as setforth in claim 3, wherein only the pump delivery pressure detecting unitis provided.
 5. A control device for a four-stroke engine as set forthin claim 3, wherein only the atmospheric pressure detecting unit isprovided.
 6. A control device for a four-stroke engine as set forth inclaim 5, wherein the atmospheric pressure detecting unit detects anatmospheric pressure from intake pressure detected by the intakepressure detecting unit.
 7. A control device for a four-stroke engine asset forth in claim 6, wherein the intake pressure detecting unit detectsat least an intake pressure resulting immediately before the intakevalve opens.
 8. A method for controlling a four-stroke engine having anintake valve between a combustion chamber and an intake port and havingat least one intake control valve for one intake port of the combustionchamber, the method comprising the steps of pressurizing a fuel in afuel tank, regulating by a regulator opened to an atmospheric pressurean upper limit value for the fuel pressurized by the pump, injecting thefuel regulated an upper limit value thereof by the regulator into theintake port, detecting an intake pressure between the intake controlvalve and the combustion chamber, performing at least either the step ofdetecting an atmospheric pressure or the step of detecting the pressureof the fuel so pressurized, and controlling the fuel injection based onat least either an atmospheric pressure detected through the step ofdetecting an atmospheric pressure or a fuel pressure detected throughthe step of detecting a fuel pressure and an intake pressure detectedthrough the step of detecting an intake pressure, wherein in the step ofdetecting an intake pressure, an intake pressure is detected a pluralityof times while the four-stroke engine completes four strokes of intakestroke, compression stroke, expansion stroke and exhaust stoke, and inthe step of controlling the fuel injection, a fuel injection time iscalculated based on at least one of a plurality of intake pressurevalues detected through the step of detecting an intake pressure so thatthe fuel is injected with an injection initiating timing according tothe fuel injection time so calculated.